1. Field of the Invention
The present invention relates to a portable Doppler fetal heartbeat measurement device and a method of use for early detection of fetal heartbeat. More specifically, this invention relates to the adaptation of an intravaginal probe for use with a standard Doppler fetal heartbeat measurement device base unit and a method of use for detection of fetal heartbeat from seven to twelve weeks gestation.
2. Description of the Related Art
Christian Doppler first described what is now known as the Doppler effect in the 19th century. In the 20th century Doppler""s principle has been harnessed in the optical, radio and ultrasound sciences to produce many useful devices. Doppler ultrasound techniques for medical diagnostic purposes are well known. For example, see Atkinson and Woodcock, DOPPLER ULTRASOUND AND ITS USE IN CLINICAL MEASUREMENT, Academic Press, New York City (1982). Also, Durley III (U.S. Pat. No. 4,413,629; issued 1983) disclosed a portable, ultrasonic Doppler device for detecting fetal heartbeat and measuring its rate. The hand-held Doppler fetal heartbeat measurement device (hereafter referred to as a conventional doppler) has since become standard equipment at nearly every obstetrics practice in the United States, because it is a useful, simple and relatively inexpensive device. The conventional doppler consists of essentially two components:(i) a hand-held probe containing one or more transducers or transducer arrays for generating and detecting ultrasonic waves; and (ii) an electronic base unit (hereafter referred to as a base unit) capable of converting the electrical signal from the probe to an audible response meaningful to the human ear. In use, the hand-held probe is held against the abdomen of a woman suspected of being pregnant, with the transducer end of the probe facing in the direction of the suspected fetus. The probe is then activated, resulting in an ultrasonic wave stream (with a typical frequency of 3 MHZ) being directed through the abdominal wall. A portion of this wave stream is reflected back to the probe. If a live fetus is present, the movement of its heart (and of blood through the heart chambers) results in a frequency shift (xe2x80x9cDoppler shiftxe2x80x9d) in the waves reflected from that region. The magnitude and sign of the Doppler shift varies with the instantaneous velocity of the sound-wave-reflecting surface and hence, if this surface is that of the fetal heart, the motion of the heart chambers. An audible signal is generated by the base unit from the varying Doppler shift. The base unit may also display a visual readout, e.g. a digital display, of fetal heart rate.
In a typical pregnancy, the conventional doppler is incapable of reliably detecting the fetal heartbeat until about 12 weeks gestation. This is owing primarily to the low level of ultrasonic energy reflected from the first trimester fetal heart and to the high degree of dampening of that energy (ultrasonic impedance) by the abdominal wall of the mother. In the event of complications, or the observation of a uterus size that does not correlate to the date of the last menstrual period, a physician""s only option to determine fetal viability is to order a sonogram with an intravaginal probe. This technique allows early visualization and measurement of fetal cardiac activity. It has significant disadvantages, however, in that it is expensive and often requires the patient to be sent to another facility which is inconvenient and delays verification of fetal viability.
The primary approach to solving this problem has been directed at increasing the signal to noise ratio of the conventional doppler. Lee et al. (U.S. Pat. No. 5,630,418; issued 1997) [xe2x80x9cLee Ixe2x80x9d] discloses a controller for muting break noise in a conventional doppler. Break noise is generated when the probe is moved across the skin surface causing the probe/skin interface to be momentarily broken. Eliminating break noise increases the signal to noise ratio and makes it easier to identify the fetal heartbeat while the physician is seeking the fetal heart (which involves moving the probe across the abdomen). Lee et al. (U.S. Pat. No. 5,827,969; issued 1998) [xe2x80x9cLee IIxe2x80x9d] teaches a device that uses an abdominal probe with selective power settings, enabling the user to increase the power of the transmitted ultrasonic energy, which increases the reflected signal from the fetal heart. Another approach has been aimed at improving the signal processing techniques used to distinguish the low level fetal heartbeat component from the background noise. While these approaches have improved the sensitivity of the conventional doppler they are inherently limited by the impedance of the mother""s abdominal wall and the distance between the probe and fetus, especially in obese patients.
The fetal heart begins beating at approximately six to seven weeks gestation. Medically, it is desirable to detect and measure fetal heartbeat in the patient""s first office visit (typically approximately eight weeks gestation). It is particularly desirable in cases of spotting, cramping, pain or other complications to determine whether fetal heartbeat is present and its nature, as a demonstration of fetal viability and as a means of reducing subsequent risk of miscarriage. Further, it offers early peace of mind for the patient, especially those with a history of miscarriage. Further still, it may lead to earlier detection of ectopic and other abnormal pregnancies, possibly allowing non-invasive treatment options and better preservation of patient fertility. As indicated above, however, present technology, though available in the form of full sonography systems, is expensive and inconvenient. The capital investment in sonography equipment is 100 to 200 times the cost of the conventional doppler that is present in every ob-gyn office, even those in rural areas of the country far from medical centers. As a consequence, the charges to the patient are comparably much more expensive. Furthermore, patients in rural areas usually have to travel to another town or city to have this procedure carried out in those instances where the early detection of fetal heartbeat is imperative. One consequence is that on many occasions where it is deemed to be helpful (and in retrospect would have been very useful) it is simply not done.
Therefore, what is needed is an inexpensive, portable device that is capable of reliably detecting fetal heartbeat and measuring its rate as early as seven weeks gestation.
It is an object of the present invention to provide an inexpensive and convenient method and device for detecting fetal heartbeat and measuring its rate in the first trimester of pregnancy. More particularly, it is the object of the present invention to provide such a method and device capable of detecting and quantifying fetal heartbeat as early as eight weeks gestation for the majority of pregnancies.
The present invention meets its objectives by adapting the conventional doppler. The present inventor has found, through experimentation, that with some modifications to the conventional probe, this new device is highly capable of detecting fetal heartbeat and measuring its rate at seven to eight weeks gestation. Consequently, one embodiment of the method of the present invention is to adapt the probe of the conventional doppler so that it can be used intravaginally. Although there are a number of probe designs for the conventional doppler, all terminate in a blunt, flat region intended to be placed against the outside of the abdomen, and then moved along the outside abdominal wall. Nevertheless, it is possible in many instances, after taking standard steps to ensure an antiseptic surface, to introduce the end of one of the conventional-doppler probes into the vagina and thereby, in many cases, obtain an early detection of the presence and rate of the fetal heartbeat. This is a procedure that has not been previously disclosed or taught.
Although it is possible to use the conventional doppler in the abovedescribed fashion, it tends to be awkward and not applicable to every woman. The device of the present invention is designed to overcome these problems, by adapting the conventional doppler to incorporate a true intravaginal probe. The intravaginal probe of the present invention contains the following elements: (I) a rigid or semi-rigid, elongated body portion, (ii) one or more transducers or transducer arrays for emitting and detecting ultrasonic energy and (iii) a means for transmitting intravaginal probe signal information to the base unit.
By using the conventional doppler base in connection with a modified probe, the device of the present invention achieves its goal of enabling every obstetrician""s office to afford a means of early fetal-heart detection. The device of the present invention will cost an amount comparable to the traditional doppler device for detecting fetal heartbeat externally through the abdominal wall: about $600 in the present market. There are a number of enhancements that can enhance the device and method of the present invention. Though these embodiments will increase the cost somewhat of the device, the total price will still be about two orders of magnitude below that of the sonography equipment to which physicians and patients must now turn to for early detection of fetal activity. The enhancements include such things as providing wireless communication between the transducer-containing probe and the electronic base unit. This would give the ultimate in hand-held convenience for the person manipulating the probe. The wireless communication would be carried out by any one of the many known methods presently in use in computer technology and elsewhere, such as radio-based, infrared-light-based and the myriad of other telemetry methods.
The method of the present invention for detecting and quantifying fetal heartbeat as early as seven to eight weeks gestation has the following steps: (i) gently insert the intravaginal probe into the vagina, (ii) activate the electronic base unit so as to produce ultrasonic waves from the probe, (iii) by manipulating the probe, direct an ultrasonic wave stream towards the suspected fetus, (iv) detect the ultrasonic waves reflected from the fetal heart at the intravaginal probe and (v) convert the signal from the intravaginal probe to an audible and/or visual display of fetal heart rate at the base unit. One advantage of the present inventive method is that the ultrasonic impedance between the intravaginal probe and the fetus during examination is low, owing to their close proximity. Therefore, the reflected signal from the fetal heart is more easily separated from background noise. This enables the fetal heartbeat to be reliably detected and its rate quantified several weeks earlier than can be achieved with the conventional abdominal method.
The present invention has been found to be useful in detecting and quantifying the fetal heartbeat in early pregnancy. This means, for example, that if complications arise early in pregnancy, e.g. 8 weeks gestation, the present invention may be used to confirm the presence of fetal heartbeat in any obstetrician""s office, without resorting to transvaginal sonography. This has the significant advantages of reducing patient expense, quickly confirming fetal viability (providing immediate peace of mind for the patient) and reducing patient inconvenience.